1. Field of the Invention
The present invention relates to a method of fabricating protective caps, and more particularly, to a method of fabricating protective caps for protecting elements on a wafer surface.
2. Description of the Prior Art
Currently, wafer level chip scale packages (WLCSP) have become one of the most popular packaging techniques. The wafer level chip scale packages are defined by having correspondingly equal or larger areas of the package structure than the area of the die. The area of the package structure is usually no larger than 25% of the die area. In general, the main difference between the wafer level chip scale package and the conventional package lies in the fact that the wafer level chip scale package first packages the wafer before the dicing process and then performs a dicing process after the packaging process to form a plurality of packaging structures. This in comparison to the conventional package wherein the wafer is diced first to form a plurality of dies and a packaging process is performed for each of the dies thereafter.
Since part of the wafer surface usually includes fragile structures, such as micro-electromechanical structures, special processes are often performed to protect the micro-electromechanical structures on the wafer surface during the packaging process of the wafer. Currently, protective caps made of metal or glass are commonly disposed on the fragile structures to protect the fragile structures from external damage. The fabrication of the protective caps can be divided into two categories. A first category and method of fabricating the protective caps involves dicing the wafer into a plurality of dies and fabricating protective caps on the surface of each die thereafter. However, this method is relatively complex and requires significantly long processing time. Hence, another wafer level package process has been introduced to fabricate the protective caps.
Please refer to FIG. 1 through FIG. 3. FIG. 1 through FIG. 3 are perspective diagrams showing a wafer level package process according to the prior art. As shown in FIG. 1, a substrate 12 is provided, in which the surface of the substrate 12 includes a plurality of fragile structures 16, such as micro-electromechanical structures. Next, a second category and method of fabricating the protective caps involves providing a cap substrate 14, in which the surface of the cap substrate 14 includes a plurality of cavities 22, such that the cavities 22 are located corresponding to the fragile structures 16. Next, the cap substrate 14 is disposed on the substrate 12, in which the cavities 22 of the cap substrate 14 are corresponding to the fragile structures 16. Preferably, the cap substrate 14 also includes a plurality of bonding media 20 disposed on the periphery region surrounding the cavities 22, and a plurality of sealed rings 18 corresponding to the substrate 12, such that the bonding media 20 and the sealed rings 18 are utilized to bond the cap substrate 14 to the substrate 12.
As shown in FIG. 2, the cap substrate 14 and the substrate 12 are diced along the direction I to form a plurality of dies 30, in which the surface of each die 30 includes a protective cap 40 disposed on each of the fragile structures 16. As shown in FIG. 3, since the surface of the substrate 12 also includes a plurality of bonding pads 24 and the bonding pads 24 are covered by the protective caps 40, another dicing process must necessarily be performed along the direction II to dice the cap substrate 14 and expose the bonding pads 24 for facilitating electrical connection thereafter.
As a result, the two dicing processes utilized in the conventional packaging process will not only increase the possibility of misalignment, but also increase damage to the die resulting from pollution caused by micro-particles. Hence, if the number of dicing operations were to be reduced, damages resulted from the dicing process could be prevented and the yield of the package process could thereby be increased.